Event Title

Effects of Turbidity on Shortwave Radiation and Instream Temperature

Presenter Information

Andrew Hobson

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

4-20-2010 10:30 AM

End Date

4-20-2010 10:35 AM

Description

Limited water resources in Southern Utah with the competing interests of humans and native fishes require careful management. High instream temperatures resulting from low flows are a consideration in managing the Virgin River for two endangered fish species. Throughout these periods, fish behavior changes have been observed during times of high turbidity. One hypothesis was that high turbidity decreased the amount of solar radiation in the water column due to increased reflection at the water surface resulting in reduced instream temperatures. To quantify the extent of changes in incoming energy to the river, a water tank was constructed to measure the effects of turbidity on solar radiation reflection off the water surface and attenuation with depth. We found that increases in turbidity led to a linear increase in solar radiation reflection for specific turbidity ranges. We also found that attenuation of solar radiation increased linearly as turbidity increased for specific turbidity ranges. The effects of turbidity on solar radiation behavior were translated into changes in instream temperatures through the use of an instream temperature model. The results indicated during summer low flow conditions that turbidity increases from 30-500 NTU decreased instream temperatures 1°C on average with maximum decreases of 2°C.

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Apr 20th, 10:30 AM Apr 20th, 10:35 AM

Effects of Turbidity on Shortwave Radiation and Instream Temperature

Eccles Conference Center

Limited water resources in Southern Utah with the competing interests of humans and native fishes require careful management. High instream temperatures resulting from low flows are a consideration in managing the Virgin River for two endangered fish species. Throughout these periods, fish behavior changes have been observed during times of high turbidity. One hypothesis was that high turbidity decreased the amount of solar radiation in the water column due to increased reflection at the water surface resulting in reduced instream temperatures. To quantify the extent of changes in incoming energy to the river, a water tank was constructed to measure the effects of turbidity on solar radiation reflection off the water surface and attenuation with depth. We found that increases in turbidity led to a linear increase in solar radiation reflection for specific turbidity ranges. We also found that attenuation of solar radiation increased linearly as turbidity increased for specific turbidity ranges. The effects of turbidity on solar radiation behavior were translated into changes in instream temperatures through the use of an instream temperature model. The results indicated during summer low flow conditions that turbidity increases from 30-500 NTU decreased instream temperatures 1°C on average with maximum decreases of 2°C.

https://digitalcommons.usu.edu/runoff/2010/Posters/14